This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Deep brain stimulation-DBS of the subthalamic nucleus-STN and globus pallidus interna (GPi) has been demonstrated to be effective in the treatment of the cardinal motor signs of Parkinson's disease-PD: tremor, rigidity, and bradykinesia. Due to early limited reports, which suggest more robust improvements in UPDRS motor scores, and the ability to reduce parkinsonian medication with STN, but not GPi, STN has been the preferred target of most centers. There is increasing evidence that STN DBS may be associated with a number of mood and cognitive changes. Because of the small size of the STN, 158mm3, stimulation within the sensori-motor area can result in spread to limbic and associative areas of STN as well as to surrounding structures and fiber systems that may also affect mood and cognition. Since the GPi, 478 mm3, is significantly larger than the STN, a lead can be placed in the sensorimotor territory of the GPi with less likelihood of current spread to non motor portions of the GPi or to adjacent structures and fiber systems that can adversely change mood and cognition. The aim of this study is to carry out a prospective clinical trial investigating the effect of STN and GPi DBS on mood and cognitive function. This study will characterize the types and incidence of mood and cognitive changes that occur during stimulation in STN and GPi. It will also compare the relative changes in mood and cognition that occur in each site and examine the role of lead location in mediating them.